The invention relates to a method of using a composition and compound with antiprotozoal activity. These methods and materials will potentiate control of protozoal populations under a variety of conditions, particularly in ruminants.
The normal diet of the ruminant animal is forage. Forage includes grasses, legumes and cellulytic byproducts of agricultural production. These are either fed fresh as pasture or green chop; in a dry form as hay; or in a preserved state as silage. The ability to utilize these materials as sources of nutrients is only possible as a result of pregastric bacterial fermentation in the rumen, the nonfundic portion of the animal's stomach. Here, bacterial action reduces the complex structural carbohydrates; cellulose, hemicellulose, and lignin and the associated nonstructural carbohydrates; pectin, starches and sugars, to either fatty acids or more chemically simplistic carbohydrate forms, which are then subjected to gastric action in the fundic stomach and small intestine.
The adaptation of ruminants to pregastric digestion has involved a system of retention of digesta, which is an essential part of the mechanism for maximal extraction of energy. This retention requires some sacrifices in food intake, which becomes more limited on forage based diets because the coarser ingests must be retained longer to achieve efficient extraction of energy. This poses a special problem in the modern, domesticated ruminant, in that the nutrient demands created by genetic selection for rapid lean muscle growth or high levels of milk production far exceed the supply generated by rumenal fermentation of forage based diets.
The diets that must be fed require the addition of large amounts of nonstructural carbohydrate (starches and sugars) fed in the form of grain which, unfortunately, often is a source of physiologic and metabolic stress.
These problems are associated with the changes which occur in rumenal fermentation as a result of grain ingestion. As a consequence, feeding strategies must attempt to maximize forage use while not compromising nutrient supply needed for maintenance and production.
A solution to the problem of nutrient supply and demand in the ruminant animal, as imposed by the limitations of bacterial, pregastric digestion, is to enhance the efficiency and rate at which this process occurs. The rumen is a continuous fermentation system that is provided with nutrients (feeds), buffers (salivary and other salts) and fluids (water and saliva) on both a continuous and an intermittent basis. The efficiency of this fermentation is measured through rumen turnover. Turnover is conventionally expressed as the portion of the rumen contents that leaves the rumen per hour. Liquids and solids turn over at different, but usually related, rates. Liquid flow rates, as proportions of the total liquid volume, have been found to turn over at rates that increased from <8 to 13.5%/hr as dry matter intake went from 5 to 21 kg/day (Livestock Prod. Sci., 17:37, 1987). At the same time, solids turnover increased from 3 to 5%/hr due to increased intake. In other studies, values of 17%/hr for liquids (Can. J. Ani. Sci., 64 (Supp.):80, 1984) and as high as 7.0%/hr for concentrates (J. Dairy Sci., 65:1445, 1982) were reported. In a typical ration of a dairy cow consuming >20 kg dry matter/day, representative rumen digesta passage rates would be 15%/hr for liquids, 6%/hr for grains and 4.5%/hr for forages. The rates would all decrease with a lower level of intake.
Another important rumen characteristic associated with turnover rate is microbial yield, where microbial yield is defined as the quantity of microbial mass flowing from the rumen per day. A further, and important refinement of this expression of microbial yield, which is also effected by turnover rate, is the efficiency of microbial yield. This is usually expressed as grams of microbial protein (or nitrogen) produced per kg of organic matter (OM) digested in the rumen. Both aspects of microbial production have applied significance. Microbial yield is important as an index of the amount of microbial protein available to the ruminant animal per day.
Microbial efficiency is important as part of the calculation of microbial yield where: microbial yield (gr of microbial N/day)=microbial efficiency (gr microbial N/kg digested organic matter)×kg OM digested in the rumen per day.
Because of the rapid rumen turnover rates commonly found in cattle with high dry matter intakes, such as dairy cattle, high microbial efficiencies are expected. If, however, an imbalance in the nutrients available to the rumen microbes occurs, the microbial efficiency can be impaired. This is particularly evident if ruminally available nitrogen or carbohydrate sources are inadequate.
Another factor which effects ruminal microbial efficiency and yield is predation by rumen protozoa. The rate of bacterial predation is proportional to the concentration of bacteria available. Coleman (The Roles of Protozoa and Fungi in Ruminant Digestion. Armidale, Penambul Books, 1989, p. 13) reported that when bacterial concentrations were 109/ml, a value representative of that in rumen fluid, the average uptake for 18 protozoal species was 493 bacteria/hr/protozoa; when bacteria were at the maximum density, the average uptake for the 18 species of protozoa was 3,739 bacteria/hr/protozoa. Protozoal predation involves engulfment which usually kills the bacteria. The overall effect of predation on bacterial numbers is considerable.
It has been shown that the removal of protozoa (defaunation) can result in a 2-4 fold increase in numbers of rumen bacteria. The reduction in bacterial numbers is not uniform across all species. Generally, more amylolytic than cellulolytic bacteria are engulfed. It is possible, therefore to conclude that the extent and rate of digestion of various carbohydrates differs between fuanated and defuanated animals. Protozoa also have negative effects on rumen function. Because of their sequestration on large feed particles and on the rumen wall, the flow of protozoa from the rumen is less than would be predicted from their concentration in the rumen and rate of digesta flow.
Therefore, although protozoa can represent 50% of the biomass in the rumen, they contribute 20% or less to the microbial protein flowing to the duodenum. In addition, predation on bacteria causes recycling of bacterial protein in the rumen. Protozoa engulf and kill large quantities of bacteria, assimilating much of the protein from these organisms.
Since most of the protozoa remain in the rumen until they lyse, microbial protein flow from the rumen also is reduced. In vivo measurements summarized by Jounay et al (Anim. Feed Sci. Tech. 21:229, 1988) indicate that defuanation resulted in a 36% increase in grs of microbial nitrogen flowing from the rumen per kg of organic matter fermented.
An additional negative aspect of protozoa on digestive function that is important to ruminants in general, and high producing dairy cows in particular, is their engulfment and digestion of particulate feed protein. This permits protozoa to assimilate proteins of low rumen degradability which have been added to the diet as sources of by-pass protein (Hoover et al. Rumen Digestive Physiology and Microbial Ecology, West Virginia University Bulletin 708T; p 22.).
The overall effects of the presence or absence of protozoa in ruminants are not well characterized because of the difficulty in reducing their numbers in viva. Compounds which have demonstrated defuanating activity have proven too toxic to safely feed to ruminants or ineffective when fed for prolonged periods of time. Thus although the benefits of defuanation have been conclusively demonstrated in vitro, the transferal of this information to field practice has yet to be accomplished.